I'm new to astrophotography (and photography for that matter). I've been looking at equipment and I have a fairly basic question about mounting a camera to a telescope or using a telephoto lens. To make this a little more concrete I came up with the following example
Telephoto Lens - Sigma 100-400mm f/5-6.3 DG DN OS
Specs: f/6.3, focal length: 400 mm, aperture: 63.5mm, price $949
Refractor Telescope - William Optics Guide Star 61 APO Refractor Telescope
Specs: f/5.9, focal length: 360 mm, aperture: 61mm, price $398
The specs seem comparable. Well, the telephoto lens is more than twice the price but I also end up with a zoom lens that I can use for the rest of my photography. There are other differences with respect to ease of mounting, detector options, etc. but my question is about the optics. Is there anything special about telescope optics that is different than for telephoto lenses?